The invention relates to a modulator-demodulator.
Modulator-demodulators are used, by way of example, in the transmission-reception paths of mobile radios. During modulation and demodulation, messages are conditioned into a signal form that ensures that the message is transmitted over the greatest possible distance while maintaining the required signal-to-noise ratio.
During modulation and demodulation based on code multiplexing such as code division multiple access (CMDA), also called spread spectrum multiplexing (SSMA), the reception path is always in operation, whereas the transmission path operates only intermittently. A level of power consumption during operation determines the maximum possible standby time. If the intention is to use only a single voltage controlled oscillator for the modulator and the demodulator, then the different frequencies required for the modulator and the demodulator results in that frequency dividers are necessary. In the case of wideband CDMA (WCDMA), a divider with a division factor of two is used to obtain, by way of example, the transmitted signal having a transmitted signal frequency of 570 MHz from the oscillator signal of a voltage-controlled oscillator with an oscillator frequency of 1140 MHz. In the A reception path, a signal with a carrier frequency of 380 KHz is required, therefore a divider with a division factor of 3 is needed when using the 1140 MHz oscillator. However, a drawback is that a divider with an uneven division factor has a higher power consumption than a divider with an even By division factor. In addition, dividers with an uneven division factor have a more asymmetrical duty cycle than dividers with an even division factor.
Published, European Patent Application EP 0 905 917 A2 specifies a modulator-demodulator, configured for GSM 900/DCS 1800 Standard, in which the carrier frequencies required for frequency mixer, modulator and demodulator are produced using a plurality of oscillators and frequency dividers. The modulator-demodulator is able to transmit and receive in different frequency bands (dual band). With GSM, transmission and reception take place in timeslots and not at the same time.
It is accordingly an object of the invention to provide a modulator-demodulator that overcomes the above-mentioned disadvantages of the prior art devices of this general type, whose power consumption is as low as possible in order to achieve the greatest standby time possible.
With the foregoing and other objects in view there is provided, in accordance with the invention, a modulator-demodulator. The modulator-demodulator contains a voltage controlled oscillator and a divider chain connected downstream of the voltage controlled oscillator. The divider chain has a plurality of series-connected dividers each with a respective even-numbered division factor. Each of the dividers produces carrier signals including a first carrier signal and a second carrier signal orthogonal with respect to the first carrier signal. A quadrature demodulator for receiving an input signal is connected to one of the dividers of the divider chain producing the carrier signals at a desired carrier frequency. A first vector modulator having mixers is connected to the dividers of the divider chain producing the carrier signals at required carrier frequencies. A further divider with an even-numbered division factor is connected downstream of the first vector modulator. A second vector modulator is provided for producing a transmitted signal. The second vector modulator is connected downstream of the further divider.
In the inventive modulator-demodulator, the voltage-controlled oscillator is provided, downstream of which the divider chain is connected. The divider chain has a plurality of series-connected dividers with a respective even-numbered division factor. Each divider produces a carrier signal and a carrier signal that is orthogonal with respect thereto. In addition, the quadrature demodulator for a received signal is provided which is connected to the divider of the divider chain that produces the carrier signal at the required carrier frequency. The first vector modulator has the mixers that are connected to the dividers of the divider chain that produce the carrier signals at the required carrier frequencies. In addition, a further divider with an even-numbered division factor is provided which is connected downstream of the first vector modulator. Connected downstream of the further divider is the second vector modulator for producing a transmitted signal.
The modulator-demodulator advantageously has a low-pass filter that is connected between the first vector modulator and the further divider. The low-pass filter can filter out disturbing signal components.
In accordance with another embodiment of the inventive modulator-demodulator, the division factors of the dividers is 2.
In accordance with another feature of the invention, the modulator-demodulator can advantageously be used in a mobile radio system.
The modulator-demodulator has a second divider connected to the demodulator and in which the first divider and the second divider are connected to the first vector modulator. This configuration is advantageously suitable for the UMTS frequency plan, specifically at an oscillator frequency fVCO=1520 MHz or fVCO=760 MHz, in particular.
The modulator-demodulator has a third divider that is connected to the demodulator and in which the second divider and the third divider are connected to the first vector modulator. This configuration is likewise advantageously suitable for the UMTS frequency plan, specifically at an oscillator frequency fVCO=1520 MHz, in particular.
The modulator-demodulator in accordance has the second divider connected to the demodulator and the second divider and the third divider are connected to the first vector modulator.
The configuration is likewise advantageously suitable for the UMTS frequency plan, specifically at an oscillator frequency fVCO=1520 MHz, in particular.
The modulator-demodulator has the first divider connected to the demodulator and in which the first divider and the second divider are connected to the first vector modulator. This configuration is likewise advantageously suitable for the UMTS frequency plan, specifically at an oscillator frequency fVCO=760 MHz, in particular.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a modulator-demodulator, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.